Image display devices hitherto installed on passenger seats of aircrafts, trains and the like are generally of a type having an image display panel, a tilt angle of which is manually adjustable so that the passenger watching the display adjusts the tilt angle of it with his hand.
FIG. 6A and FIG. 6B show one example of such conventional image display devices installed on seats of an aircraft, a train or the like. FIG. 6A shows one aspect, for instance, wherein a tilt angle of an image display panel is being adjusted when backrest 421 of the front seat equipped with the image display device is reclined while viewer 401 keeps his backrest 402 in the upright position. Viewer 401 pulls image display panel 425 toward him to increase tilt angle θT around tilting pivot 424 and adjust it in a manner to set image display panel 425 generally perpendicular to a direction of his viewing axis. FIG. 6B shows another aspect, wherein the tilt angle of the image display panel is being adjusted when backrest 421 of the front seat is in the upright position while the viewer reclines backrest 402 of his seat. Viewer 401 pushes image display panel 425 to decrease tilt angle θT in the same manner to adjust image display panel 425 generally perpendicular to the direction of his viewing axis.
In this connection, various methods have been proposed in recent years for making adjustment of tilt angle of the image display panel automatically. Patent literature 1, for instance, discloses one such method. FIG. 7A and FIG. 7B illustrate the method. The method disclosed in this example uses linkage mechanism 550 for adjusting the tilt angle of image display panel 525, as shown in FIG. 7A. While viewer 501 stays with his backrest 502 in the upright position, when backrest 521 of the front seat is reclined, linkage mechanism 550 operates to increase a tilt angle of image display panel 525 to a degree proportional to an inclination angle of backrest 521. This completes automatic correction of the angle of image display panel 525 with respect to the direction of viewing axis of the viewer.
The conventional method of manually adjusting the tilt angle of the image display panel has a drawback, however, that, in many cases, viewer 401 is unable to reach image display panel 425 on the front seat with his hand unless he raises himself when backrest 402 of his seat is reclined low. Viewer 401 is therefore required to repeat raising himself and adjusting the tilt angle of image display panel 425 several times in order to obtain the optimum tilt angle. In addition, the tilt angle needs to be readjusted whenever a person in the front seat changes the reclining angle of his seat. The same is true when the viewer changes the reclining angle of his own seat. Changing of the reclining angle of the seats hence gives the user a troublesome task of adjustment, and it puts a significant burden upon him.
There are also some drawbacks with the another conventional method of making correction of the tilt angle of image display panel 525 simply with linkage mechanism 550 installed in the seat, that it leaves a problem in terms of adjusting accuracy of the angle besides the limitation in a range of the correctable angles against different viewing conditions of various users. Image display panel 525 provides generally a good viewability, in particular, when viewer 501 keeps backrest 502 of his seat not inclined. However, when viewer 501 reclines backrest 502 of his seat while backrest 521 of the front seat remains reclined as shown in FIG. 7B, the condition of viewability becomes poorer since this results in a large deviation of the viewing axis of the viewer from the direction perpendicular to the screen of image display panel 525.    Patent Literature 1: Japanese Patent Unexamined Publication, No. 1990-105752